It's looks a lot like a dolly (the kind of dolly you use for moving heavy boxes), but with larger wheels. Segways are motorized, designed to transport people in a manner that's safer and more environmentally-friendly than that of cars.

Not to be confused with a segue, of the same pronounciation, which is a transition between two consecutive ideas in a speech or conversation.

"I guess I thought about trying a Segway, but bicycles are so much cheaper."